Electric devices such as motors and generators having a stator secured within a housing of the motor/generator are well known. A rotor mounted on a shaft is coaxially positioned within the stator and is rotatable relative to the stator about the longitudinal axis of the shaft to transmit the force capacity of the motor. The passage of current through the stator creates a magnetic field tending to rotate the rotor and shaft.
Some stators are generally configured as an annular ring and are formed by stacking thin plates, or laminations, of highly magnetic steel. A copper winding of a specific pattern is configured, typically in slots of the lamination stack, through which current is flowed to magnetize sections of the stator assembly and to create a force reaction that causes the rotation of the rotor.
Bar pin stators are a particular type of stator that include a winding formed from a plurality of bar pins, or bar pin wires. The bar pin wires are formed from a heavy gauge copper wire with a rectangular cross section and generally configured in a hairpin shape having a curved section and typically terminating in two wire ends. The bar pins are accurately formed into a predetermined shape for insertion into specific rectangular slots in the stator, and are typically coated with an insulating material prior to insertion, such that the adjacent surfaces of the pins within the slots are electrically insulated from each other.
Typically, the curved ends of the bar pins protrude from one end of the lamination stack and the wire ends of the bar pins protrude from the opposite end of the lamination stack. After insertion, the portions of the wire protruding from the lamination stack are bent to form a complex weave from wire to wire, creating a plurality of wire end pairs. Adjacent paired wire ends are typically joined to form an electrical connection by welding one wire end to its adjacent or paired wire end to form a welded joint, where each pair of wires is individually welded, for example, by arc welding. The resultant weave pattern and plurality of welded joints determines the flow of current through the motor. To facilitate welding of the wire ends, the wire ends of the bar pins are typically stripped of insulation prior to insertion into the lamination stack and bending into the weave pattern. Electrical conductivity and structural integrity of the welded joint between each of the paired wire ends is a key determiner of motor quality and performance. Joint quality can be affected by the geometry of the wire ends, cleanliness of the wire surfaces prior to welding, defects such as porosity and microcracks introduced into the weld, spatter produced in the arc welding process, the cross-sectional or surface area of the weld and other factors. Joint quality can also be affected by variation in the positioning of the adjacent wire ends as a result of the bending process, where spacing and proximity of the wire ends to each other may contribute to variability in the welded joint. Frequent tooling adjustment or limited tool life may be required during the wire bending process to maintain the tight tolerances required to accurately position the wire ends for the welding operation. The process of arc welding each wire pair joint individually is time consuming and may produce inconsistent welded joints. Variability in the process and configuration of each wire end pair results in variability in the electrical connection of each wire end pair. This may result in thermal variation in the operation of the motor, localized overloading of the welded joint causing an electrical discontinuity, e.g., a short, in the winding due to, for example, welds of minimal surface or cross-sectional area or with a small heat-affected zone, or due to weld splatter between wire end pairs.